A Marantz analog tuner is on my bucket list, but if I buy another tuner my wife will kill me. Catch-22! Right? I'm finely down to two Marantz tuners. At one time I had 5 Marantz tuners. I still have a Realistic tuner and a Dynaco FM3 tuner. So down to 4 tuners. That's pretty good for me. :D
audiokarma.org
As far as I can tell, when Marantz switched production of the model 20 to the 20B, they did not restart the serial number sequence. I believe the serial number on the first 20 B is not #1.
I believe they added the B to the serial number later, after some B units had already been produced.
So I believe the sequence was:
1. Model 20 with serial numbers starting with 20
2. Model 20B with serial number starting with 20
3. Model 20B with serial number starting with 20B
I presume that all Model 10B production had ceased by the time the 20B was introduced. That would suggest a change to Marantz serial number policy added B to the serial number tag long after the introduction of the 10B. Confused yet?
I bet somebody in the Marantz forum will know. According to the Vacuum Tube Valley article, 94 Marantz model 10 tuners were produced before the 10B.
IMHO Marantz decided that the letter B was a marketing advantage and they seem to have zealous about adding it to later models.